That's the problem right there. In Cataclysm, Blizzard's philosophy will be "Bring the talent tree, not the talent(s) or spell(s). What that means is that after they redesign the talents and trees for Cata, their aim is for players to make simpler choices about talents to the point that all they'll need to do is pick a tree and go with it. There will also be less hand wringing about picking secondary talents in other trees. You will simply pick one tree and go deep into it.

Having sub or hybrid specs has never been something encouraged by Blizzard. From a development perspective, they're difficult to support and balance for. Invariably, when a viable hybrid spec is discovered, it quickly becomes the FOTM and everyone suddenly switches to it. Builds like Frostfire and SL/SL (and shockadin to a much lesser extent) are like the chemistry experiments that resulted in something unique and exciting instead of exploding in our faces.

Right, but when I do a chemistry experiment, I WANT something new and exciting! What's the point in a game that tries not to be fun and exciting? Just defeats the purpose!

Here's the thing, WOW isn't a chemistry experiment. It's a Chemistry Factory. When things get too new and exciting in the home it's....not necessarily so bad. When things get new and excited in a factory it can be devastating.

@uncaringbear

You are correct that Blizzard does not encourage hybrid specs - but subspecs certainly are encouraged and expected. Any tree with so many attractive talents that most players consistently put most of their talent points in a single tree are branded as bloated, and eventually consolidated and pruned. However, frostfire is *not* a hybrid spec. It is a full fire spec that takes 51+ points in fire, and puts its excess points in frost, instead of arcane. It would be a completely "normal" spec for any other class - the only reason it was interesting for mages is the historical incompatibility of the frost and fire trees, while arcane was the neutral tree that complemented either.